1. Field of the Invention
The present invention generally relates to printed circuit boards and, more particularly, to a printed circuit board having a structure to correct warpage, a printed circuit board assembly in which electronic parts are mounted on such a printed circuit board, a manufacturing method of a printed circuit board for manufacturing a printed circuit board while correcting warpage, a manufacturing method of a printed circuit board assembly for manufacturing a printed circuit board assembly by mounting electronic parts while correcting warpage, and a correcting method for correcting warpage of a printed circuit board.
2. Description of the Related Art
When mounting electronic parts to a printed circuit board, the electronic parts may not be mounted well if there is a deformation such as warpage in the printed circuit board. When warpage of a printed circuit board causes a problem, it is necessary to mount electronic parts to the printed circuit board while acquiring flatness by correcting the warpage.
There are suggested the following method to correct warpage of a printed circuit board in a mounting process.
1) Electronic parts are mounted after flatten a printed circuit board by mounting the printed circuit board on a flat placement surface of a conveyance carrier, arranging a warpage correction press block on a side of a part mount head, and pressing the printed circuit board onto the flat placement surface of the conveyance carrier by the press block immediately before mounting the electronic parts.
2) Electronic parts are mounted to a printed circuit board by arranging many warpage correction pins in a part mounting mechanism part and while correcting warpage of the printed circuit board by pressing the warpage correction pins onto the printed circuit board.
3) Printed circuit board is placed on a flat placement surface of a conveyance carrier and fastened by screws.
In the above-mentioned methods, it is required to acquire a part for pressing pins onto a part of a printed circuit board or a part for fasting screws, thereby reducing an effective area of a printed circuit board.
Moreover, a surface of a printed circuit board may get scratches due to a contact of the pressing pins, which generates dusts. Also in the case of screw fastening, screws and a conveyance carrier are in friction with each other, which may generate dusts. Those dusts contaminate printed circuit boards and electronic parts. If the dusts are electrically conductive substances, there is a problem in that they short-circuit electronic parts and between terminals of the printed circuit boards. Or, there is a problem in that the ducts enter a joining part between an electronic part and a printed circuit board, which deteriorates bonding reliability.
Furthermore, in the methods of 1) and 2), although warpage of the printed circuit board is in a corrected state when mounting electronic parts, the printed circuit board tends to return to an original warped state immediately after the pressing block or the correction pins are separated from the printed circuit board. Accordingly, for example, since cure of a bonding material to join electronic parts is not progressed sufficiently, a force to return the printed circuit board to an initial warped state is exerted, and, thus, there may be a problem in that the bonded part is separated.
In order to solve the above problems, there is suggested a method of correcting warpage of a printed circuit board by clamping a peripheral part of the printed circuit board between a conveyance carrier and a warpage preventing metal fitting (for example, refer to Patent Document 1 and Patent Document 2). Additionally, there is suggested a method of mounting electronic parts in a state where a printed circuit board is applied to a conveyance carrier by using a pressure-sensitive adhesive double coated tape (For example, refer to Patent Document 3).    Patent Document 1: Japanese Laid-Open Patent Application No. 2002-57451    Patent Document 2: Japanese Laid-Open Patent Application No. 11-46060    Patent Document 3: Japanese Laid-Open Patent Application No. 3-163896
According to the method of correcting warpage of a printed circuit board by clamping a periphery of the printed circuit board between a conveyance carrier and a warpage preventing metal fitting, a problem of material taking of a printed circuit board is solved since warpage is corrected by clamping a periphery of the printed circuit board, which is not an effective area. Additionally, since the printed circuit board can be fixed to a conveyance carrier even after mounting electronic parts, warpage of the printed circuit board can be corrected until a bonding material is cured sufficiently after mounting. However, since the printed circuit board is clamped by a warpage preventing metal fitting, the problem of generation of dusts due to contact of the warpage preventing metal fitting is not solved. Additionally, a work of clamping a periphery of a printed circuit board by a warpage preventing metal fitting is a troublesome work.
On the other hand, according to the method of mounting electronic parts in a state where a printed circuit board is applied to a conveyance carrier by using a pressure-sensitive adhesive double coated tape, there is a problem in that the double coated tape is deformed when an electronic part is pressed onto a printed circuit board and also the printed circuit board is deformed since the double coated tape is arranged between the conveyance carrier and the printed circuit board. Additionally, it is necessary to peel off the printed circuit board from the double coated tape after mounting electronic parts, and an external force, which may deform the printed circuit board when peeling off, may lower the mounting reliability.